cmd/compile: unreachable code causes internal compiler error

[jrick]

Go version

go version go1.22.0 openbsd/amd64

Output of go env in your module/workspace:

GO111MODULE=''
GOARCH='amd64'
GOBIN=''
GOCACHE='/home/jrick/.cache/go-build'
GOENV='/home/jrick/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='amd64'
GOHOSTOS='openbsd'
GOINSECURE=''
GOMODCACHE='/home/jrick/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='openbsd'
GOPATH='/home/jrick/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/home/jrick/src/go'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='local'
GOTOOLDIR='/home/jrick/src/go/pkg/tool/openbsd_amd64'
GOVCS=''
GOVERSION='go1.22.0'
GCCGO='gccgo'
GOAMD64='v1'
AR='ar'
CC='clang'
CXX='clang++'
CGO_ENABLED='1'
GOMOD='/dev/null'
GOWORK=''
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
PKG_CONFIG='pkg-config'
GOGCCFLAGS='-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build3442254126=/tmp/go-build -gno-record-gcc-switches'

What did you do?

https://go.dev/play/p/NHe6QNjlr_i

What did you see happen?

CLOSURE [prog.go:13:9:var n int]
<unknown line number>: internal compiler error: assertion failed

Please file a bug report including a short program that triggers the error.
https://go.dev/issue/new

What did you expect to see?

No build error (except for unreachable code warnings from vet).

[thanm]

Thanks for the report.

cc @golang/compiler

[jrick]

this also affects non-loop labels https://go.dev/play/p/ylEUvtiBb1X

[jrick]

the general pattern here seems to be:

1. early unconditional return
2. declare a variable
3. declare a label
4. use the variable after the label. assignments to _ will trigger the bug. For loop labels, the variable usage can occur either inside the loop, or after.

We hit this in our "real code" due to an early unconditional return that was added near the top of a function to stub out something that wasn't ready yet.

[thanm]

Duplicate of #65593?

[jrick]

Yes, appears to be.